The autonomic nervous system controls the involuntary smooth and cardiac muscles and glands throughout the body, serving the vital organ systems such as the heart that function automatically. The two divisions (sympathetic and parasympathetic) of the autonomic nervous system oppose each other in function, thus maintaining balanced activity in the body mechanisms. For example, signals generated in the hypothalamus, cerebral cortex and medulla oblongata within the brain and transmitted via the parasympathetic fibers of the vagus nerve to the sino-atrial node of the heart slow the heart rate while signals along the sympathetic fibers accelerate the heart rate. An imbalance in the relative activity of the sympathetic and parasympathetic divisions of the autonomic nervous system, for example, an increase in the activity of the sympathetic division, can produce abnormal heart rates in the form of tachycardias or fibrillations in either or both chambers (ventricles and/or atria) of the heart.
It is well known that the electrical stimulation of the parasympathetic nerves innervating the heart can restore autonomic nervous system balance by counteracting arrhythmias produced by increased sympathetic activity. Thus, electrical stimulation of the right vagus nerve predominantly slows the S-A node rate and thereby reduces heart rate. The vagus nerve, and particularly cardiovagal branches thereof, are found chiefly adjacent to the posterior surface of the vena cava. Accordingly, parasympathetic activity may be increased to restore autonomic balance by electrically stimulating the fibers of the vagus nerve transvenously by means of an endovascular electrode implanted in, for example, the superior vena cava.
There remains a need for a suitable endovascular, vagus nerve-stimulating lead for chronic use in the areas of discrimination, rate slowing, termination, prediction and prevention. Such a lead would desirably incorporate an array of electrodes adapted to be arranged along the longitudinal direction of the vena cava, with positionally stable placement or anchoring of the electrode array within the vena cava.